Methods of repairing cavities caused by caries and the like include generally the following methods.
The first one is a repairing treatment method using a prosthesis such as a crown or inlay with a material called a luting cement, and the second one is a repairing treatment method using a filling material such as a composite resin with an adhesive resin.
Representative luting cements used today in the above method include a glass ionomer cement, a resin-reinforced glass ionomer cement and a resin cement. It is explained that the glass ionomer cement may bond to tooth substance by chelate bond and that the sustained-release of fluorine from the cement inhibits the progress of caries by helping the recalcification of tooth substance and by inhibiting the sugar metabolism and acid production by Streptococcus mutans. However, any conclusive evidence of the adhesion is not yet provided and there is no clear presentation on the effective concentration and sustained-release period of fluorine which may contribute to the recalcification. In addition, the glass ionomer cement has problems that the physical properties of the cement per se are deteriorated when the cement is contacted with moisture such as saliva at the early stage of curing, and above all, the cement is decomposed under wet and acidic conditions usually encountered in the oral cavity, causing secondary caries.
With the above problems, there have been disclosed various resin-reinforced glass ionomer cements for which the issue of water-sensitive properties is especially considered (Patent Documents 1, 2 and 3). These are compositions made by blending a glass ionomer cement component with a monomer having a polymerizable ethylenically unsaturated double bond and a polymerization catalyst. It is considered that the decomposition of the cement under the conditions in the oral cavity is reduced by the addition and polymerization of the resin component (polymerizable monomer and polymerization catalyst). However, a fundamental solution is not achieved.
On the other hand, it is accepted that the resin cement does not have water-sensitive properties unlike the glass ionomer cement and is excellent in tooth substance adhesion. However, stable tooth substance adhesion is not obtained unless the teeth are treated by surface treatment, primer treatment or the like with an acidic aqueous solution such as phosphoric acid. Especially, a cut dentin surface is frequently wet with an exudate and the like and therefore the pretreatment before the bonding is complicated. It may be considered that the resin cement is a technique-sensitive material and requires skills in handling.
Commercially available resin cements are divided into two types: one is a chemically polymerizable resin using a redox initiator composed of a peroxide and an amine compound, and the other is a dual-cure resin in which the redox initiator is combined with a photo-polymerization initiator. Both types have chemical polymerizability in case they are applied to area where light will not reach, for example in case they are used to bond an inlay, a crown and the like and to build an abutment. For this reason, there are problems that they are susceptible to polymerization inhibition by water, oxygen and the like under an oral cavity environment and the polymerizability is reduced at the bonding interface due to the exudates especially when the resin cements are applied to the dentin surface. Such problems often cause secondary caries. In addition, the polymerization heat generated at the time of polymerization is unpleasant for patients, and the resin derived from the amine compound is discolored with time.
Further, as the second repairing treatment method, there has been proposed a dental adhesive composition and a kit for repairing cavities using an adhesive resin (Patent Document 4). This composition is composed of a polymerizable monomer, a polymerization initiator, a reducing agent and water. However, camphorquinone is essential as a polymerization initiator in order to ensure sufficient bonding performance and durability to teeth, and further at least a given amount (0.01% by weight) of camphorquinone based on the composition is required.
[Patent Document 1] Japanese Patent Application Publication No. H6-27047
[Patent Document 2] Japanese Patent Laid-Open Publication No. H8-26925
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2000-53518
[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-238325